Bad notice is often a reason for loss of copyright. The first season of "Star Trek" was released for sale on a multitude of videos, since a Vice-President (who soon lost his job) did't do that job correctly
From what I understand, Desilu was the reason why the copyright notice didn't appear on the first season of Star Trek. Paramount bought Desilu before the second season started. It wasn't until the 80's that they realised that there's no copyright on season one and got a retro-active copyright installed.